U.S. patent number 5,932,720 [Application Number 09/011,845] was granted by the patent office on 1999-08-03 for solid sucralose.
This patent grant is currently assigned to Tate & Lyle Public Limited Company. Invention is credited to George Henry Sankey.
United States Patent |
5,932,720 |
Sankey |
August 3, 1999 |
Solid sucralose
Abstract
The flowability of crystalline sucralose can be increased by
treating the crystalline material in a fluidised bed at ambient
temperature with additions of water, followed by a fluidised drying
phase. Fluidisation by means of an upward current of air at
25-35.degree. C. and added water at 20-50% by weight, e.g., 25-40%,
is preferred.
Inventors: |
Sankey; George Henry (Earley,
GB) |
Assignee: |
Tate & Lyle Public Limited
Company (GB)
|
Family
ID: |
10779664 |
Appl.
No.: |
09/011,845 |
Filed: |
February 18, 1998 |
PCT
Filed: |
July 18, 1996 |
PCT No.: |
PCT/GB96/01729 |
371
Date: |
February 18, 1998 |
102(e)
Date: |
February 18, 1998 |
PCT
Pub. No.: |
WO97/08181 |
PCT
Pub. Date: |
March 06, 1997 |
Foreign Application Priority Data
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|
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|
|
Aug 23, 1995 [GB] |
|
|
9517281 |
|
Current U.S.
Class: |
536/124; 536/122;
536/127; 536/123.13 |
Current CPC
Class: |
C07H
5/02 (20130101) |
Current International
Class: |
C07H
5/00 (20060101); C07H 5/02 (20060101); C07H
001/00 () |
Field of
Search: |
;536/4.1,119,124,127,123.13,122 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
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|
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1543167 |
|
Mar 1979 |
|
GB |
|
2065646 |
|
Jul 1981 |
|
GB |
|
Primary Examiner: Peselev; Elli
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb &
Soffen, LLP
Claims
I claim:
1. A method of treating crystalline sucralose to remove fines and
to modify the size and shape of individual crystals so as to lower
the angle of repose and to increase the flowability, comprising
fluidizing the crystalline material in a fluidised bed at a
temperature of 25-35.degree. C. with additions of water, followed
by drying the crystalline material while it is fluidised.
2. A method according to claim 1, in which fluidisation is achieved
by an upward current of a carrier gas.
3. A method according to claim 1 or 2, in which water is added at a
rate of from 20-50% by weight of material during a treatment time
of up to 4 hours.
4. A method according to claim 3, in which water is added at a rate
of from 25-40% by weight of material during a treatment time of 15
minutes to 2 hours.
5. A method according to claim 3, in which water is added at a rate
of from 25-30% by weight of material during a treatment time of 1
to 1.5 hours.
6. A method according to claim 5, in which the starting material
has an average diameter of 100-200 mm, a coefficient of variation
(CV) of particle size of at least 48% and an angle of repose of
38-48.
7. A method according to claim 4, in which the starting material
has an average diameter of 100-200 mm, a coefficient of variation
of particle size of at least 48% and an angle of repose of
38-48.degree..
8. A method according to claim 3, in which the starting material
has an average diameter of 100-200 mm, a coefficient of variation
of particle size of at least 48% and an angle of repose of
38-48.degree..
9. A method according to claim 2, in which the starting material
has an average diameter of 100-200 mm, a coefficient of variation
of particle size of at least 48% and an angle of repose of
38-48.degree..
10. A method according to claim 1, in which the starting material
has an average diameter of 100-200 mm, a coefficient of variation
of particle size of at least 48% and an angle of repose of
38-48.degree..
11. A method according to claim 2, in which water is added at a
rate of from 20-50% by weight of material during a treatment time
of up to 4 hours.
12. A method according to claim 11, in which the starting material
has an average diameter of 100-200 mm, a coefficient of variation
(CV) of particle size of at least 48% and an angle of repose of
38-48.degree..
13. A method according to claim 11, in which water is added at a
rate of from 25-40% by weight of material during a treatment time
of 15 minutes to 2 hours.
14. A method according to claim 13, in which the starting material
has an average diameter of 100-200 mm, a coefficient of variation
of particle size of at least 48% and an angle of repose of
38-48.degree..
15. A method according to claim 11, in which water is added at a
rate of from 25-30% by weight of material during a treatment time
of 1 to 1.5 hours.
16. A method according to claim 15, in which the starting material
has an average diameter of 100-200 mm, a coefficient of variation
of particle size of at least 48% and an angle of repose of
38-48.degree..
Description
This invention relates to the preparation of solid crystalline
sucralose having improved flow characteristics and appearance.
Sucralose (4-chloro-4-deoxy-.alpha.-D-galactopyranosyl
1.6-dichloro-1.6-dideoxy-.beta.-D-fructo-furanoside, otherwise
known as 4,1', 6'-trichloro4, 1',6'- trideoxyealacto sucrose) is a
potent sweetener originally disclosed in GB 1543167. Crystalline
sucralose was disclosed in GB 2065646A in the form of orthorhombic
needles. It is a problem of crystalline materials of this type.
that because the needle-like structure tends to bind together to
form mats, thev are thus difficult to transfer from one container
to another. It is difficult to produce free-flowing sucralose, even
under closely controlled laboratory conditions, and on large scale
plant the problem is aggravated by the fact that the subsequent
processing equipment such as pumps, centrifuges and drvers tends to
fracture the crvstals, thus further harming the flow properties.
There is thus a need for pure sucralose having a modified structure
with improved flow properties.
The flow behaviour of solids is conventionally assessed in terms of
flow speeds and also in terms of the angle of repose of the poured
material. In Bulk Solids Handling: An Introduction To Practice And
Technology, by C R Woodcock and J S Mason, Leonard Hill, Julv 1987,
page 31, the flow behaviour of particulate solids is crudely
classified in terms of the angle of repose as follows:
25 -30.degree. very free-flowing
30 -38.degree. free-flowing
38 -45.degree. fair
45-55.degree. cohesive
Greater than 55.degree. very cohesive
From this it will be seen that a free-flowing material should have
an angle of repose not exceeding about 38.degree. and it is an
object of the present invention to provide sucralose having an
angle of repose tvpically below 40.degree. and preferably within
the range of 34 -38.degree.. Flow behaviour for a particulate solid
can also be more directly measured by a funnel test in which a
sample of the material is timed as it flows through a funnel of
known dimensions (as described below with reference to the Examples
and in Bulk Solids Handling (ibid)).
We have now found that crystalline sucralose obtained directly from
the final crystallisation stage of the synthetic process can be
treated by a simple operation using standard equipment to provide
considerably enhanced flow characteristics. The nature of the
changes taking place in the material appear to be relatively
complex and varied. It appears that the treatment removes fines and
modifies the size and shape of individual crystals, providing a
narrower particle size distribution and crystals of a chunkier,
more cubic shape. The treated product may actually have a larger
overall particle size, but this is not always the case. In
particular, it should be noted that the process is not an
agglomeration process in which small particles become stuck
together, but more a process of crystal redefinition.
According to the present invention there is provided a method of
treating crystalline sucralose to remove fines and to modify the
size and shape of individual crystals so as to lower the angle of
repose and to increase the flowability, comprising treating the
crystalline material in a fluidised bed at ambient temperature with
additions of water, followed by drying the crystalline material
while it is fluidised. Typically, fluidisation is achieved by an
upward current of an appropriate carrier gas, typically air. The
process can be carried out in conventional fluidised bed drivers
and granulators for example the MP2 (Niro Limited) which consists
of four main areas:
an inlet air conditioning system:
modularised containers for the above applications;
a liquid dosing system; and
an exhaust air system.
The drying air is drawn in by a fan through an inlet filter and
heated by passing it over a steam heat exchanger. Temperature
control is achieved by mixing hot air from the heat exchanger with
ambient air via a valve.
The sucralose is placed in the product container and fluidised in a
stream of warm air. The water is sprayed using a top spray two
fluid nozzle onto the fluidised bed. The product is therefore
modified and dried in one operation.
The water is fed to the nozzle using a peristaltic pump. The
exhaust air is passed through a filter to prevent the product
leaving the process chamber. The amount of water added, and the
length of time of treatment may be varied within relatively wide
ranges to provide products of particular specifications. In
general, water should be added at a rate of from 20-50%, preferably
25-40%, most preferably 25-30% by weight of material during a
treatment time of up to 4 hours, typically from 15 minutes to 2
hours. e.g. from 1 to 1.5 hours, at a bed temperature of, say,
25-35.degree. C., e.g. about 30.degree. C. before the final drying
step.
Preferably, the starting material is screened to remove outsize
pieces, and typical starting materials will have an average
diameter of 100-200 mm. a co-efficient of variation (CV) of
particle size of at least 38-48% (although material with a
co-efficient of variation as low as 44% can still be improved) and
an angle of repose of 38-48.degree..
As described in Crystallisation. 3rd Edition, J W Mullin,
Butterworth and Heinemann, 1993. particle size distributions (PSDs)
may be conveniently classified by the median size and the
coefficient of variation. The CV. which quantifies the size spread
is a statistical property related to the standard deviation of a
Gaussian distribution and is normally expressed as a percentage by
##EQU1##
The values of L.sub.84%, L.sub.50% (=L.sub.M) and L.sub.16% may be
obtained from a cumulative mass distribution curve. The higher the
CV the broader the spread, CV =0 denoting a single-sized
distribution. The CV for a Gaussian distribution is 52%, but the
product from a sugar crystallizer, which generally conforms more to
a gamma function distribution. has a CV of about 50%.
The PSDs were measured by laser light scattering using the Malvern
Mastersizer.
By way of example, a number of experiments were carried out using
four different starting materials, SM1, SM2, SM3 and SM4, generally
at a scale of approximately 12 kg. Examples 6 and 10 show the
results of smaller scale experiments with higher amounts of water
added.
The angle of repose was measured as the poured angle of repose
(i.e. the angle between the horizontal base and a sloping side of a
conical heap poured gently from a funnel onto a flat surface. The
speed of flow was measured as follows.
Equipment
Powder funnel with a stem 25 mm in length and 22 mm in
diameter.
Stop clock
Procedure
1. Place the funnel in a stand such that the top of the stem is 20
cm above the height of the bench.
2. Weigh 50 g of sample into a clean dry 500 ml beaker.
3. Insert a bung into the bottom of the funnel and then pour the
weighed sample into the top of the funnel. Place the beaker under
the stem.
4. Remove the bung and record the time taken for the sample to pass
through the stem. Repeat this measurement twice more and record an
average of the three timings.
5. If some sample remains adhering to the funnel, record the weight
of sample which passes through the stem. This will give an
indication of the amount of sample remaining in the funnel.
6. If the sample does not flow through the stem. tap the top of the
funnel. If this causes the sample to pass through the funnel, the
timings should be repeated with the top of the funnel being gently
tapped. A note that tapping was necessary must be recorded
alongside the timings. If the material does not pass through the
funnel even with tapping, it should be reported as not flowing.
Table 1 shoes the typical running conditions, illustrated for
Examples 1, 2, 3 and 5, while Table 2 shows the results obtained
for Examples 1 to 11.
It will be seen that the treatment considerably reduces the angle
of repose and provides good flow characteristics. Furthermore, the
product obtained is generally a shiny crystalline material of
bright appearance, resembling caster (fine crystal) sugar.
TABLE 1 ______________________________________ OPERATIONAL DATA AND
TEST RESULTS Example No. 1 2 3 5
______________________________________ Starting Material SM1 SM1
SM1 SM2 Temperature During Spraying Inlet (.degree. C.) 62-63 62-64
62-66 64-66 Bed (.degree. C.) 28-28 29-35 29-35 26-37 Exhaust
(.degree. C.) 25-27 26-27 26-28 24-31 Duration of Spraying 1 h 17 m
1 h 18 m 1 h 16 m 1 h 8 m Temperature During Drying Inlet (.degree.
C.) 63 62 62 61-66 Bed (.degree. C.) 28-38 29-39 29-39 26-39
Exhaust (.degree. C.) 25 27 26-28 23 Duration of Drying 6 m 4 m 4 m
5 m Atomizing Pressure (bar g) 2.0 2.0 2.0 2.0 Amount of Water 3200
3200 3200 3200 Added (g) Spray Rate (g/min) 39-45 40-43 40-43 43-50
Charge Weight (kg) 12.388 12.420 12.400 12.433 Final Weight (kg)
11.574 12.680 12.509 11.807 Moisture (%)* 0 0 0 0
______________________________________ *Determined by loss in
weight on a Mettler Infra Red Moisture Meter at 55.degree. C./10
mins
TABLE 2
__________________________________________________________________________
Resdiual Angle of Flow Scale PSD (microns) Bulk density g/ml Water
H.sub.2 O repose test Batch (kg) D(L.sub.16%) D(L.sub.84%)
D(.sub.L.sub.50%) CV % Test 1 Test 2 added (%) (degrees) (Sec)
__________________________________________________________________________
SM1 61.0 185.2 117.1 53.1 0.74 0.8 <0.1 42.8 <2 Ex 1 12.4
69.8 177.7 118.2 45.7 0.74 0.85 26 <0.1 -- <2 Ex 2 12.4 60.9
173.5 109.7 51.4 0.75 0.85 26 <0.1 36.2 <2 Ex 3 12.4 65.4
173.7 112.9 48.0 0.76 0.87 26 <0.1 -- <2 Ex 4 12.4 71.7 188.3
123.0 47.4 0.75 0.85 26 <0.1 -- <2 SM2 114.0 283.0 191.0 44.2
0.82 0.89 -- 38.5 <2 Ex 5 12.4 157.0 337.0 240.0 37.5 0.75 0.82
26 <0.1 35.2 <2 SM3 76.1 220.5 147.6 48.9 0.72 0.78 <0.2
46.2 no flow Ex 6 0.96 61.0 202.3 129.5 54.5 0.8 0.9 40 <0.5 --
1 Ex 7 12.5 103.8 246.6 163.9 43.5 0.76 0.87 26 0.14 36.7 <1 Ex
8 12.5 100.5 239.9 162.5 50.8 0.74 0.87 26 0.17 38 2 <1 Ex 9
12.5 115.1 280.1 180.3 38.7 0.76 0.87 26 0.18 37.2 <1 SM4 61.5
193.3 118.0 55.8 0.69 0.73 0.1 45.5 no flow Ex 10 1.0 60.9 186.6
116.3 54.0 -- -- 40 -- 36.4 -- Ex 11 11.5 72.8 200.7 124.8 51.2
0.77 0.84 26 <0.1 36.4 <2
__________________________________________________________________________
* * * * *